Washing bars can be classified into three categories: (1) soap bars; (2) mixed active bars containing a significant proportion of soap; and (3) synthetic detergent bars containing only a small proportion of soap or none at all.
Conventional soap bars comprise a large proportion, typically 60-80% by weight, a fatty acid soap. Fatty acid soaps are selected to provide a balance of soluble and insoluble soaps which provide the required functional properties as regards lather formation and bar structure. Conventional soap bars are manufactured by milling, plodding and stamping a semi-solid mass of soap and other components.
Bars known which contain a mixture of soap and synthetic detergent where the amount of soap may be less than the amount of synthetic detergent, but is nevertheless still a significant contributor to the content of the bar. In such bars, as in conventional soap bars, the content of soap, especially the insoluble soap, contributes to the structure and physical properties of the bar.
The third category is synthetic detergent bars, often known as "Syndet" bars, in which there is no soap or only a small amount and the detergent active is mostly or wholly a synthetic, non-soap, detergent. Generally such bars contain a substantial proportion of material which is not a detergent, but which serves to give structure to the bar. Such "structurants" are normal water-insoluble and include such materials as starch and kaolin. The bars frequently also contain a plasticizer: known plasticizers include stearic acid and cetyl alcohol. Known surfactants for syndet bars include primary alkyl sulphates, alkyl ether sulphates, betaines, sarcosinates, sulphosuccinates and isethionates.
These syndet bars containing no soap or only a small proportion of soap are traditionally produced by energetic working of a physical mix of structurant (e.g., starch), plasticizer (e.g. stearic acid) and sudactant (e.g., acyl isethionate), i.e., both the soluble and insoluble components, in a high shear mixer to an end point at which the product is not gritty. The mix is then formed into `syndet` bars.
The known process has several disadvantages in that the physical mixing step is performed batchwise and requires an energetic mixer.
In a copending case, U.S. Ser. No. 08/213,287 to Chambers et al. assigned to the same assignee as the subject invention, the inventors were able to dispense with the known energetic working step by using a specific combination of ingredients comprising:
(a) 10-60 by wt. of a synthetic non-soap surfactant (e.g., isethionate or SLES); PA1 (b) 10-60% by wt. of a water-soluble structurant having a melting point in the range of 40.degree.-100.degree. C. (e.g., polyethylene glycol); PA1 (c) 5-50% by wt. of a water insoluble structurant having a M.P. of 40.degree.-100.degree. by. wt. PA1 (d) 0-20% by wt. water. PA1 (1) about 35% to 70% of a normally solid, water-soluble, anionic synthetic surfactant; and PA1 (2) about 22% to 50% normally solid fatty vehicle with melting point between 120.degree. F. and 220.degree. F. selected from a group including higher fatty acids (e.g., stearic) and ethylene glycol. PA1 (a) 10-60%, preferably 10-40%, more preferably 10-35% by weight of a synthetic, non-soap detergent; PA1 (b) 10-60%, preferably 20-50% by weight of a water-soluble structurant which is neither soap nor a non-soap detergent and which has a melting point in the range 40.degree.-100.degree. C.; PA1 (c) 5-50% by weight of a water-insoluble structurant which is neither soap nor a non-soap detergent and which has a melting point in the range 40.degree.-100.degree. C.; PA1 (d) 1 to 25%, preferably 5 to 15% of a water soluble starch; PA1 (e) 1 to 14%, preferably 1 to 9% by weight water; PA1 non soap synthetic detergent which does not completely liquify at temperatures below 100.degree. C., for example acyl isethionates; PA1 soap, especially water insoluble soap, which does not melt below 100.degree. C.; PA1 other water insoluble materials which do not melt below 100.degree. C.
At page 8 of the specification it is said that water-insoluble structurant (component (c)) having a melting point above 100.degree. C. may also be used (i.e., to strengthen bar and reduce smearing) but that it should comprise, if used at all, no more than 20% by wt. of the composition. Starches are one of the materials mentioned for possible use and it is noted that corn starches, for example, are preferred.
Unexpectedly, applicants have found not only that such starch materials are required (i.e, to increase mixer viscosity and billet hardness), but that not all starches are equal. That is, applicants have recognized that the starch must not be just a "partially soluble" material such as corn starch or potato starch but that it must be a "true" water soluble material such as, for example, maltodextrin in order to obtain user benefits (i.e., smoother, non-grittier surface).
By "true" soluble is meant the starch should dissolve to clear or hazy/clear solution at 10% by wt. or greater of the starch in water at room temperature (in contrast to other starches such as corn or potato starch which, at room temperature, swell, but which do not dissolve).
U.S. Pat. No. 2,987,484 to Lundberg, teaches a bar made by a closed die molding technique which bar comprises:
In Lundberg, polyethylene glycol is not used at all as a water-soluble structurant (only ethylene or di-ethylene glycol). Although used as additives (additives are used up to about 10% according to column 12, line 72 and either 5% or 9.3% in Examples), they ordinarily are not used in an amount 10 to 60% as in the invention, let alone in preferred amounts of 20-50% by wt.
Lundberg is not concerned with the problem of energetic mixing (since it is a closed die molding technique) and simply does not recognize the advantage of using the water soluble structurants (e.g., PEG) of the invention in the amounts required. Further, Lundberg certainly does not teach or suggest that use of particular types of starches are also required or that some starches are better than others.
U.S. Pat. No. 5,225,097 to Kacher et al. teaches skin pH freezer bars comprising (1) 10 to 50% free fatty acids; (2) 15 to 65% of an anionic and/or nonionic bar firmness aid which may include PEG; and (3) 15 to 40% water; wherein the pH is about 4.8 to 6.0.
The bars of the subject invention cannot contain this amount of water because the bars would simply become too soft to process. The bars of the invention can have no more than 14% water content, preferably no more than 10% water.
The reference also clearly does not appreciate the need of added starch, nor that some starches are superior to others (i.e., the starches must be "truly" water soluble).
The unique combination of ingredients of the invention yielded a bar which is firmly structured and yet has a smooth non-gritty surface without excessive smear properties.